Toner Fixing Apparatus

Abstract: A resistance film (30) which generates heat when a power is supplied is wound around a roller so that a roller may be rotated. An impression roller, which comes in contact under pressure with the resistance film, is provided and rotated synchronized with the resistance film an opposite direction. A printing form is transferred between and by the resistance film and the depression roller. In this case, toner delivered onto the printing form is fixed by supplying the power to the resistance film. The resistance film can be of an endless type or a web type.

Description: The present invention relates to a fixing apparatus for fixing toner transferred onto a medium in electronic photograph IC recording equipment such as photocopiers, laser printers and facsimile machines and, more particularly, to a fixing apparatus for melting and fixing toner. For conventional electronic photograph recording equipment, there have been commonly available two types of apparatuses for fixing toner transferred onto a medium; one is a pressure fixing apparatus which pressurizes a medium while passing it between two rollers and the other is a thermal fixing apparatus which fixes toner while applying a pressure to the medium and melting it by heat from the rollers or the like. In a pressure fixing apparatus which pressurizes the medium with pressure rollers, it is difficult to fix toner on a medium with irregularities, and moreover, a pressure fixing apparatus normally requires excessively large pressure to pressurize a medium, and therefore, a thin medium will be easily broken. Furthermore, to uniformly pressurize a medium in its widthwise direction, the diameter of the pressure rollers should be increased and the bearings which support the pressure rollers should also be large- sized and a large pressure roller driving force is duly required. On the other hand, in some of thermal fixing apparatuses, a heat source is incorporated in respective pressure rollers, or a medium is heated by a xenon lamp or the like without touching the medium. However, thermal fixing apparatuses will require a large capacity heat source and consume significantly large power. Therefore, such thermal fixing apparatuses remain in danger of combustion at all times during use. Though these thermal fixing apparatuses are used in a large number because they are relatively congenial to any kind of medium, for example, it takes a lot of time to thermally start up the apparatuses, they cannot fix toner immediately. Moreover, the thermal fixing apparatuses require a large capacity heat source, and therefore, they are required to have provisions for heat discharging, fire prevention, and safety. As described above, there have been problems which prevent both pressure fixing and thermal fixing apparatuses from being reduced in size. EP-A-0 505 030 discloses a fixing apparatus fixing a toner on a recording material by using joule heat which is generated by applying a voltage across the conductors or across the electrodes to supply a current mostly to a fixing portion. This fixing apparatus does not include an arrangement of the electrodes in combination with the arrangement of the nip as disclosed in the present invention. The document US-A- 5 084 738 discloses a fixing apparatus having an electrical conductive film, which moves in contact with the recording material on which a picture image is held, a pressing roller for causing the film to be brought into contact with the recording material, and a plurality of electrodes disposed along a nip between the film and the pressing roller at a position opposing this pressing roller. Also, this document does not disclose an arrangement of the electrodes in combination with the arrangement of the nip as it is realized in the present invention. An object of the present invention is to provide a fixing apparatus whose thermal efficiency is improved by using the maximum possible part of heat generated by a heat source in melting toner. Another object of the present invention is to provide an economical, excellent fixing apparatus which permits improving thermal efficiency and downsizing. A further object of the present invention is to provide a fixing apparatus whose heat source is free from wear and provides durability. To attain the above objects, a fixing apparatus according to the present invention is constructed as claimed in claims 1 and 6. When the pressure-holding members are formed by a pair of rollers, a plurality of electrodes are arranged as the roller at the heat generating resistance film side in the widthwise direction of the heat generating resistance film, and a low resistance heat conducting film is provided between the heat generating resistance film and the medium, a current flows in the direction of the thickness of the heat generating resistance film between the roller-type electrodes and the low resistance film, thus causing the heat generating resistance film to produce heat, and the toner is fixed. Since the heat generating resistance film generates heat only when required and is cooled in a relatively short time, the heat discharging mechanism and several types of safety mechanisms can made simple and compact. Therefore, the printer apparatus can be downsized and low-priced. Further advantageous embodyments of the invention are claimed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an approximate side view showing an electronic photograph printer provided with a fixing apparatus according to a first embodiment. Fig. 2 is a partly cutaway perspective view showing a fixing apparatus according to the first embodiment. Fig. 3 is a cross sectional view showing the fixing apparatus according to the first embodiment. Fig. 4 is an illustration showing a main unit of the fixing apparatus according to the first embodiment. Fig. 5 is a cross sectional view showing a fixing apparatus according to a second embodiment. Fig. 6 is a cross sectional view showing a fixing apparatus according to a third embodiment. Fig. 7 is an illustration showing a fixing apparatus according to a fourth embodiment. Fig. 8 is an illustration showing a main unit of the fixing apparatus according to the fourth embodiment. Referring to the accompanying drawings, preferred embodiments according to the present invention are described in detail below. Components common to all drawings are given the same number or symbol. A first embodiment is described below. In Fig. 1, an electronic photograph printer 1 such as a laser printer, having a fixing apparatus of the first embodiment is provided with an electronic photograph recorder 2, form feed rollers 4, and form transfer rollers 5 and further equipped with a form feed cassette 6 and a form ejecting cassette 7. The electronic photograph recorder 2 comprises an exposure drum 8, a charging unit 9, an exposure head 10, a developing unit 11, a transcribing unit 12, and a cleaning unit 13. In the electronic photograph recorder 2, the surface of the exposure drum 8 is uniformly charged by the charging unit 9 as it rotates, and the exposure head 10 forms an electrostatic latent image according to printing data. The electrostatic latent image is developed by the developing unit 11 and is visualized with toner. On the other hand, a form 14 which is fed from the form feed cassette 6 by the form feed rollers 4 is transferred by the form transfer rollers 5 to a printing position. A toner image formed on the exposure drum 8 is transcribed onto the form 14 by the transcribing unit 12. Then the form 14 is transferred to the developing unit 11. The fixing apparatus 21 fixes toner on the form 14, which is then ejected into the form ejecting cassette 7. The operation of the first embodiment is described below. In Fig. 1, the form 14 fed from the form feed cassette 6 by the form feed rollers 4 is transferred by the form transfer rollers 5 to a toner transcribing position. A toner image formed on the exposure drum 8 through a sequential electronic photograph process is transcribed onto the form 14 by the transcribing unit 12. Then the form 14 is transferred to the fixing apparatus 21. Referring to Figs. 2, 3, and 4, the first embodiment according to the present invention is described below. In Figs. 2 and 3, a fixing apparatus of the first embodiment is provided with two resistance films 52 and 53 formed in separate loops. The resistance film 52 which is made of a material having a low resistance and high heat conductivity, such as, for example, an aluminum and copper alloy, is extended with tension between tension rollers 54 and 55 and an electrode roller 56. The tension rollers 54 and 55 and the electrode roller 56 are rotatably supported by frames 24 and 25. A gear 57 mounted on the shaft of the tension roller 54 is engaged with a gear 59 connected to a motor 58. In other words, the tension roller 54 is rotated by the motor 58. The low resistance film 52 is moved around the tension rollers 54 and 55 and the electrode roller 56. The resistance film 53 with a high resistance value, is extended between a tension roller 60 and the electrode roller 56 so as to contact the low resistance film 52 only at the electrode roller 56. A gear 61 which is mounted on the shaft of the electrode roller 56 is engaged with a gear 36 mounted on an impression roller 34 and is rotated by a motor 37. The motors 58 and 37 are controlled so that the high resistance film 53 and the low resistance film 52 are transferred at the same speed. The form 14 onto which the toner is transferred is guided between the low resistance film 52 and the impression roller 34 with the toner bearing surface of the form facing the low resistance film. Referring to Fig. 4, the electrode roller 56 is described below. The electrode roller 56 which is rotatably supported by the frames 24 and 25 comprises an assembly of a plurality of axially aligned electrode segments or first electrodes 56a of identical size which are slightly separated by insulators in the form of thin shield plates, not shown, to prevent a current from flowing between the electrode segments 56a. Brushes 62 are provided so that they respectively come into sliding contact with an electrode segment 56a. The brushes 62 are connected in parallel with a power supply 33. Since the electrode segments 56a are each in contact with the high resistance film 53, a current from the power supply 33 flows via the brushes 62 and the electrode segments 56a in the direction of the thickness of the high resistance film 53 over the entire range of its width. Power from the power supply 33 is selectively controlled by a power control part 65 in terms of time and position. Second electrodes in the form of brushes 63 are provided below both ends of the low resistance film 52 so that they come into contact with the low resistance film 52 in the nip 70. The brushes 63 are connected through a switch 64 to the power supply 33. The operation of the first embodiment is described below. The form 14 onto which a toner image is transcribed is transferred to a fixing apparatus 51 and is guided between the low resistant film 52 and the impression roller 34. At this time, the low resistance film 52 is already driven by a motor 58 in the arrowhead direction D shown in Fig. 3 and the impression roller 34 is already rotated by the motor 37 in the arrowhead direction B shown in Fig. 3. The current from the power supply 33 is applied to each of the electrode segments 56a comprising the electrode roller 56. In Fig. 4, a current flows from the electrode segments 56a to the high resistance film 53 and further from the high resistance film 53 to the low resistance film 52. In other words, as shown in Fig. 4, a current flows through the high resistance film 53 in the direction of its thickness, thus causing the high resistance film 53 to generate heat. A current flowing in such a manner, even if its amount is relatively small, allows the high resistance film 53 to generate heat; that is, the heat generation efficiency of the high resistance film 53 is increased. A current from the high resistance film 53 to the low resistance film 52 flows through the low resistance film 52 in its widthwise direction to the brushes 63. Heat generated by the high resistance film 53 melts toner on the form 14, and molten toner is fixed. It is preferable that the electrode segments 56a comprising the electrode roller 56 be made as small as possible; however, the size of the electrode segments 56a can be appropriately determined because of restrictions on electrode fabrication. Referring to Fig. 5, a second embodiment according to the present invention is described below. In the fixing apparatus of the second embodiment shown in Fig. 5, a high resistance film 68 and a low resistance film 52 are formed integral with each other are wound on a tension roller 54, a tension roller 55, and an electrode roller 56 with the high resistance film 68 inside. Brushes 63 are provided so that they come in contact with the low resistance film 52. Other arrangement of the second embodiment is the same as in the case of the first embodiment. In the second embodiment, as in the first embodiment, the high resistance film 68 generates heat when a current applied from the electrode roller 56 flows through the high resistance film 68 in the direction of its thickness. The heat generated causes the toner to be fixed. The second embodiment has a simpler structure than the first embodiment because the former has a reduced number of rollers on which the high resistance film 68 is wound, compared with the latter. Referring to Fig. 6, a third embodiment according to the present invention is described. In Fig. 6, the fixing apparatus 71 of the third embodiment has high and low resistance films as in the cases of the first and second embodiments and both resistance films are made as a web in elongated sheets. In other words, the high resistance film 72 which is wound around a takeup roller 73 and an unwinding roller 74 is intended to be wound up around the takeup roller 73, which is rotated by a motor not shown. The low resistance film 75 which is wound around a takeup roller 76 and an unwinding roller 77 below the high resistance film 72 is intended to be rolled around the takeup roller 76, which is rotated by the motor not shown. The low resistance film 75 is made of the same material as that of the first embodiment. Both resistance films 72 and 75 which are sandwiched between an electrode roller 56 and an impression roller 34 are transferred at the same speed. The form 14 onto which toner is transferred is guided between the low resistance film 75 and the impression roller 34. The electrode roller 56 which comprises a plurality of electrode segments as in the case of the first embodiment generates heat to melt and fix the toner when a current is applied to the electrode roller 56. It goes without saying that the third embodiment thus configured has the same effect as the above-described first and second embodiments. Referring to Figs. 7 and 8, a fixing apparatus of a fourth embodiment according to the present invention is described below. In the fixing apparatus of the fourth embodiment of Figs. 7 and 8, a high resistance film 82 and a low resistance film 83 are formed integral with each other with the high resistance film 82 located outside, and the high resistance film 82 is brought into contact with a divided electrode 85. The high resistance film 82 generates heat when the power is supplied. The low resistance film 83 is made of aluminum or the like as those of the above embodiments. A roller 84 which is rotatably supported by frames 24 and 25 is attached with a gear 88. This gear 88 which is engaged with a gear 36 mounted on the impression roller 34 is rotated by the motor 37 in the arrowhead direction shown in Fig. 10 and transfers the form 14 together with the impression roller 34. As shown in Fig. 8, the electrode 85 consists of a As shown in Fig. 8, the electrode 85 consists of a plurality of electrode segments or first electrodes 85a, arranged in the lengthwise direction of the roller 84, each being kept in sliding contact with the high resistance film 82 in front of its contact point with the form 14 in the nip 70. Thin insulator in the form of shield plates 90 are provided between the electrode segments 85a as in the case of the third embodiment so that no current flows between the electrode segments 85a. As shown in Fig. 8, one end of the low resistance film 83 protrudes from the high resistance film 82 and a second electrode in the form of a brush 86 is provided in sliding contact with the protruded end 83a. A current applied by the power supply 33 flows from the electrode segments 85a to the high resistance film 82. Since the electrode segments 85a are provided over the almost entire range of the width of the high resistance film 82, a current flows over the nearly overall width of the high resistance film 82 in the direction of its thickness, thus causing the high resistance film 82 to generate heat. A current flows in the widthwise direction of the high resistance film 82 to the low resistance film 83. The power from the power supply 33 is selectively controlled by an power control part 87 in terms of time and position. The high resistance film 82 which generates heat in front of its contact point with the form 14 is depressed against the form 14 while generating heat. The high resistance film 82 is depressed against the form 14 to melt the toner on the form 14 and fix thereon. It is preferable that the low resistance film 83 be formed to be relatively thin to prevent heat generated by the high resistance film 82 from escaping in the circumferential direction of the roller 84. This roller 84 is preferably made of a material, such as, for example, ceramics with a low thermal conductivity. All the electrode segments 85a can be powered at a time, but it is also possible to select the time of current application and the electrode segments to which a current is applied, according to printing data. Power consumption can be reduced by selectively supplying power to the electrode segments 85a.

Claims: A fixing apparatus for fixing a toner onto a toner bearing surface of a medium, comprising: an electrode roller (56) having a plurality of axially aligned successively adjacent segments, the segments forming respective first electrodes (56a) and being insulated from each other; a pressure roller (34) closely opposing said electrode roller (56) so as to define a nip (70) therebetween; a heat generating high resistance film (53, 68, 72) movably disposed between said electrode roller (56) and said pressure roller and having a first surface contacting each of said first electrodes; a heat conducting low resistance film (52, 75) movably disposed between said pressure roller (34) and said high resistance film (53, 68, 72), and contacting said high resistance film (53, 68, 72) at least in said nip; at least one second electrode electrically contacting said low resistance film (52, 75) adjacent to said nip (70); and means for transporting said high and low resistance films (53, 68, 72 ; 52, 75) and the medium between said electrode roller (56) and said pressure roller, with the medium between said pressure roller (34) and said low resistance film (52, 75) and the toner bearing surface of the medium in contact with said low resistance film (52, 75) in said nip (70), whereby heat generated in said high resistance film (53, 68, 72) in said nip (70) is conducted through said low resistance film (52, 75) to the toner bearing surface of the medium, thereby to fuse the toner to the toner bearing surface of the medium. A fixing apparatus according to claim 1, wherein said high (53, 68, 72) and low resistance films (52, 75) are formed in respective first and second loops which contact each other only at said electrode roller (56). A fixing apparatus according to claim 1, wherein said low resistance film (52, 75) is formed substantially of a material selected from the group of materials consisting of copper alloy and aluminium. A fixing apparatus according to claim 1, wherein said low (52, 75) and high resistance films (53, 68, 72) comprise elongated sheets. A fixing apparatus according to claim 1, wherein said high (53, 68, 72) and low resistance films (52, 75) are integral with each other. A fixing apparatus for fixing a toner onto a toner bearing surface of a medium comprising: a resistance roller (84) having a peripheral surface; a heat conductive low restistance film (83) coating the peripheral surface of said resistance roller (84); a heat generating high resistance film (82) coating said low resistance film (83); a pressure roller (34) closely opposing said resistance roller (84) so as to define a nip (70) therebetween for receiving the medium with the toner bearing surface facing said high resistance film (83); and means for applying electrical current to the high resistance film (83) to generate heat in said nip (70), including a plurality of first electrodes (85) insulated from each other and electrically contacting said high resistance film (83), and a second electrode (86) electrically contacting said low resistance film (82). A fixing apparatus according to claim 6, wherein said resistance roller (84) is formed of a material having less thermal conductivity than said high and low resistance films (82, 83). A fixing apparatus according to claim 6, wherein said material of said resistance roller (84) comprises a ceramic. A fixing apparatus according to claim 6, further comprising switch means for applying electrical current to said first electrodes (85) selectively.

Inventors: ISOBE MINORU, ISOBE, MINORU, ISOBE, MINORU, C/O OKI ELECTRIC INDUSTRY CO.,LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1994
Main classification: G03G15
IPC codes: G03G15